For those having trouble. Here is my guide, how to finish every enemy.
First of all:
- playing through with strong and good covered characters like William Wallace:
Allways use your Sword or Sword and Shield. Defend, let the enemy attack you. Press 3 times X. Repeat. Should work against every enemy. Some characters use combos like 3 times Y. Or YAA etc.
Works with William Wallace, Alexander the Great, Attila the Hun, Genghis Khan, Hannibal, Hernan Cortez, Vlad the Impaler.
Hint: Allways hold an eye on your and your enemies stanima. When your enemies stanima is low, attack all you can!

- playing through with fast characters like Zulu and Sun Tzu:
1. Try to defend and grab. Press Y. If the enemy counters, run for your life. Get new stanima. Repeat. Should work against all strong enemies, as they are really slow.
2. If you are fighting against a fast enemy, let the enemy use up all its stanima. Attack using 3 times X. Repeat.

PS: Fights against Alexander can allways be solved by pushing him down the hole in the center of the map.